The requirements which have to be fulfilled by lithography increase in proportion to an increase in the component density of electronic circuits. The smaller the structural dimensions become, the more critical is the depth of focus of the image. It is old and well known to compensate for topographic height differences of an integrated circuit (IC) surface prior to exposure. For this purpose, a bilayer technique is used as well as several other techniques. The bilayer technique first comprises the application of a lower layer, which is also referred to as bottom resist, to a surface of the IC by means of a planarizing spin-on method. This lower layer consists of a carbon compound, which is resistant to the fluorine and chlorine, and which does not show any photosensitive. Due to this planarizing layer, the unevenness of the resultant surface lies within the depth of focus of the image. The upper lacquer film, also referred to as top resist, which is sensitive to UV and/or electron beam radiation can now be applied. The exclusive means for accomplishing the above described process is the spin-on technique. Once the upper layer has been exposed to ultraviolet light or electron beam radiation and has been developed, it serves as a mask for the bottom resist. Hence, the top resist must be resistant to O.sub.2 -RIE (oxygen reactive ion etch) and should contain the highest possible percentage of silicon and silicon dioxide, in addition to the reactive functional groups.
Until now, the upper lacquer layer or top resist lacquer has been prepared by complicated methods, and has been applied to the surface of the wafer as a thin polymer layer by means of the known centrifugal method, i.e., the so-called spin-on technique. Depending on the desired fields of use with respect to exposure wavelength and sensitivity, the following functional groups may be incorporated into the top resist lacquers for the centrifugal method: ethoxy (--OC.sub.2 H.sub.5), hydroxy (--OH) with catalyst, vinyl (--CH.dbd.CH.sub.2), chloromethyl (--CH.sub.2 Cl), phenylallyl, chloromethylphenethyl and Si--Me.
The preparation, production and processing by the centrifugal method, as well as the examination of the exposure and mask properties are disclosed in the following publications:
Novel Si-Containing Resist, Y. Yamashita, M. Kaziwara, J. Electrochem. Soc., Band 137, No. 10, Oct. 1990, pages 3253 to 3257; PA1 Submicron Pattern Transfer with New Designed E-Beam Resist and Bias-ECR Etcher, S. Sogito, S. Ishida, Y. Iida, Microelectronic Engineering 9, 1989, pages 533 to 536; PA1 Polysiloxanes with Pendant Cinnamoyl Groups as a Negative Deep UV Resist for Bilayer Applications, C. Rosilis, A. Rosilio, and B. Serre-Monanda, J. Electrochem. Soc., Vol. 136, No. 8, August 1989, pages 2350 to 2354; PA1 A Comparison for the E-Beam Sensitivities and Relative O.sub.2 -Plasma Stabilities of Organosilicon Polymers, E. Babich et al., Microelectronic Engineering 9, 1989, pages 537 to 542; and PA1 Novel Process for Direct Delineation of Spin on Glass (SOG), A. Imai et al., Jap. J. of Appl. Physics, Vol. 29, November 1990, page 2653. PA1 vaporizing a vinyl-containing substance and a linear or cyclic siloxane; and PA1 depositing these vaporized substances onto the substrate to be masked. PA1 dosing the substances with the aid of liquid mass flow control means; PA1 vaporizing the substances; PA1 distributed introduction of the vaporized substances in a reaction chamber by means of a discharge shower; and PA1 reaction of the substances in an HF field.
Many processes are not suitable for having the top resist lacquer applied by means of the centrifugal method. For example, the centrifugal method or spin-on technique is not suitable for use with cluster tools. In the field of semiconductor technology, the term cluster tool describes a system comprising a central manipulator located within a vacuum area which is provided in the system. A cluster tool is not to be confused with a plurality of separate units which are arranged in a clean room. The central manipulator is adapted to have supplied thereto wafers in a charging box, whereupon it will feed the wafers to a plurality of processing stations and tools, respectively, depending on the processes to be carried out. Methods which are suitable for use with cluster tools must not include any wet processes, and must not take place in the ambient atmosphere.
It is the object of the present invention to provide a method for applying a lacquer film, sensitive to UV and/or electron beam radiation, to a substrate to be masked so it can be employed in a wider range of applications.